The goal of this project is to translate recent advances in our understanding of activation of the EGF receptor (EGFR) into improved therapies for patients with colorectal cancer (CRC). Two complementary strategies will be employed: inhibition of the proximal events of EGFR activation (EGFR "axis") and combined inhibition of EGFR and Src. We and others have generated preclinical data and championed the notion that one can combine blockade of discrete steps in the activation of EGFR - cell surface ligand cleavage, ligand uptake by the receptor and receptor tyrosine kinase activity - to achieve cooperative growth inhibition in CRC. A Phase l/ll trial combining cetuximab and erlotinib (Tarceva") has been approved by the Cancer Therapy Evaluation Program (CTEP) and will evaluate the biological and clinical effect of this strategy. We are encouraged by preliminary data recently presented by Baselga and co-workers in which combined EGFR inhibition with cetuximab and gefitinib demonstrated significant clinical activity in patients with CRC. The second approach that will be studied in both the laboratory and clinic will be to inhibit both EGFR and Src. Src is an attractive target in CRC since Src activity is increased in 80-90% of colorectal tumors. We present genetic and pharmacological evidence that combined inhibition of EGFR and Src activity results in cooperative reduction in intestinal tumor burden and growth. The Specific Aims of Project 1are Aim 1: To evaluate the clinical and biological effects of inhibiting the EGFR axis in advanced CRC; Aim 2: To evaluate the clinical and biological effects of inhibiting EGFR and Src in a neoadjuvant trial of CRC patients with liver-limited metastasis prior to surgical resection; Aim 3: To explore novel imaging modalities in the mouse that will assess tumor volume, DNA replication, apoptosis, angiogenesis and EGFR status in a non-invasive manner. The most promising of these imaging modalities will be advanced to human application during the course of this funding cycle, These studies will be enhanced by utilizing 1) global phospho (<j))-tyrosine fingerprinting;and 2) mice in which human EGFR has been knocked into the mouse EGFR locus. Results from these studies will be used to improve the diagnosis and treatment of patients with CRC and may be applicable to other solid tumors that rely on EGFR and Src signaling.